1. Field of the Invention
The present invention relates to a navigation system for carrying out a navigation operation by using map data, and more particularly relates to a navigation system having a hard disc for storing the map data.
2. Description of the Related Art
There is a navigation system, which has a DVD-ROM (DVD-Read Only Memory) drive or a CD-ROM (Compact Discxe2x80x94Read Only Memory) drive, reads map data stored in a DVD-ROM or a CD-ROM as a record medium, and carries out a navigation operation. When carrying out the navigation operation, the navigation system detects a self-car position, reads the map data around the car from the record medium, and then displays a map picture generated on the basis of the map data together with a mark indicative of the self-car position on a display screen.
On the other hand, it may be considered that the navigation system is equipped with, for example, a hard disc, as a non-volatile memory having a large capacity, besides the record medium. If the map data of the DVD-ROM or the like is installed in the hard disc, and then the map data is read from the hard disc at a time of the navigation operation, the DVD-ROM or the like can be used for another purpose. Also, since an access speed for the hard disc is very fast, this has a merit from the viewpoint of a fast drawing on a display screen.
By the way, the DVD-ROM has a large storage capacity i.e., as large as 4.7 Gigabytes in a case of a one-surface one-layer type, and 8.5 Gigabytes in a case of a one-surface two-layer type. Thus, there arises a considerable amount of waste if a storage area of such a large storage capacity is reserved in the hard disc just to deal with the map data in, when considering the usage of the hard disc for another purpose. It is therefore desirable to limit the storage capacity reserved for storing the map data of the hard disc, and to selectively store only the map data necessary for the navigation operation.
However, it is not easy to judge in advance the portion of the map data necessary for the navigation operation among the map data stored in the DVD-ROM or the like. Further, in case that the map data supposed to be used is stored in the hard disc in advance, an empty storage area to newly store the map data necessary for the navigation operation afterward may run short. When it happens, although the data judged by the user to be unnecessary may be selectively erased so as to reserve the empty area of the hard disc, this would induce a time and labor consuming operation for the user.
The present invention is proposed in view of the above mentioned problems. It is therefore an object of the present invention to provide a navigation system, which has a hard disc, can transfer map data required for the navigation operation to the hard disc and can automatically erase the map data not required for the navigation operation, so that the user""s operation can be easily performed and the storage area of the hard disc can be efficiently utilized.
The above object of the present invention can be achieved by a navigation system for detecting a present position of a movable body and performing a navigation for the movable body on the basis of map information. The navigation system is provided with: a storage device of non-volatile type capable of writing the map data thereinto and reading the map data therefrom; a map data transferring device for obtaining the map data corresponding to a predetermined area, and transferring and storing the map data corresponding to the predetermined area to the storage device; an empty area judging device for judging whether or not an empty storage area having a predetermined capacity is reserved in the storage device when the map data transferring device is to transfer the map data corresponding to the predetermined area to the storage device; and an erasing device for determining unnecessary data among data stored in the storage device on the basis of a predetermined condition, and erasing the unnecessary data from the storage device if the empty area judging device judges that the empty storage area is not reserved.
According to the navigation system of the present invention, the navigation system is provided with the storage device, such as a hard disc or the like. In operation, the map data corresponding to the predetermined area, such as a peripheral area of the present position or the like, is obtained and transferred to the storage device. At this time, it is judged whether or not the empty storage area enough to store the map data to be transferred is reserved in the storage device. Then, if it is judged that the empty storage area runs short, the unnecessary data is determined on the basis of the predetermined condition, and the determined unnecessary data is erased from the storage device.
Therefore, the new map data to be transferred can be written into the storage device, whose empty storage area is certainly increased by erasing the unnecessary data. Thus, it is possible to avoid such a situation that the new map data cannot be stored in the storage device because the total amount of the map data exceeds the capacity of the storage device. In this manner, since the unnecessary data is automatically judged, it is easy and comfortable to use the navigation system of the present invention. Further, the storage area of the storage device is not occupied at a more than enough level, and the map data can be efficiently used.
In one aspect of the navigation system of the present invention, the navigation system is further provided with a map data reading device for accommodating a record medium, in which the map data is recorded, and reading the map data from the record medium.
According to this aspect, the navigation system is provided with the map data reading device for reading the map data from the record medium, such as a DVD-ROM, a CD-ROM or the like, so that the map data read from this record medium is transferred and stored to the storage device. Therefore, once the transferring process is performed, after that, it is not necessary to set the record medium for the map data to the map data reading device. This is very convenient for the user. Further, even if the transferring processes are repeatedly performed while exchanging the record medium one after another, since the map data is stored into the storage device after erasing the unnecessary data, it is possible to always use the new and useful map data.
In another aspect of the navigation system of the present invention, the erasing device determines the unnecessary data among the map data transferred and stored in the storage device.
According to this aspect, if the empty storage area is not reserved when the map data is to be transferred, the unnecessary data is determined among the map data stored in the storage device, and is then erased. Therefore, it is possible to keep the storage capacity for the whole map data in the storage device in a constant range, so that it is possible to continue the navigation without harmfully influencing the various data other than the map data stored in the area other than the map data storage area.
In this aspect, the erasing device may determine the map data corresponding to an areal block, which is the farthest from the present position, as the unnecessary data.
By constituting in this manner, if the empty storage area is not reserved when the map data is to be transferred, the distance between the present position and the areal block corresponding to each block map data is respectively obtained, and the map data in the areal block farthest from the present position is erased as the unnecessary data. Therefore, since the possibility that the movable body travels through the areal block, which is far from the present position, is relatively low as compared with a near areal block, it is possible to store the map data, having the higher usability in the storage device.
Alternatively in this aspect, the erasing device may determine the unnecessary data on the basis of management information, which is correlated with the map data stored in the storage device.
By constituting in this manner, if the empty storage area is not reserved when the map data is to be transferred, the management information is referred to, which is correlated with the respective map data stored in the storage device, and the unnecessary data is erased on the basis of the management information. Therefore, it is possible to determine the map data to be erased on the basis of the management information, such as access information, data type information etc., as for the respective map data, so that the usability of the map data stored in the storage device can be improved.
In this case, the management information may include the number of accesses for the map data stored in the storage device, and the erasing device may determine the map data, the number of accesses for which is the minimum, as the unnecessary data.
By constituting in this manner, if the empty storage area is not reserved when the map data is to be transferred, the number of accesses included in the management information is referred to, and the map data, the number of accesses for which is the minimum, is erased as the unnecessary. Therefore, since the map data whose usage frequency in the past navigation operation is low is selectively erased, the map data whose usability is relatively large is kept in the stored device.
In this case of using the management information, the management information may include date and time of access for the map data stored in the storage device, and the erasing device may determine the map data, the date and time of access for which is the oldest, as the unnecessary data.
By constituting in this manner, if the empty storage area is not reserved when the map data is to be transferred, the date and time of access included in the management information is referred to, and the map data, the date and time of access for which is the oldest, is erased as the unnecessary. Therefore, since the map data corresponding to the areal block where the user has never traveled for a long time is selectively erased, the map data whose usability is relatively large with reflecting the possibility of usage is kept in the stored device.
In the aspect of having the map data reading device, the storage device may be capable of writing and reading the map data at an access speed faster than that of the map data reading device.
By constituting in this manner, since the access speed of the storage device is higher than that of the map data reading device, it is possible to speedily perform the transferring process and the erasing process of the map data, so that the speedy navigation operation can be performed.
In this case, the storage device may include a hard disc device.
By constituting in this manner, since the hard disc device is used as the storage device, it is possible to utilize the storage device by transferring the map data to the storage device, which is speedily accessible, which has a large storage capacity and whose flexibility is high.
Further in this case, a map data storage area for storing the transferred map data may be set in the storage device.
By constituting in this manner, a certain storage area of the storage device is set as the map data storage area, and the transferred map data is stored into the map data storage area. Therefore, even if the storage capacity of the map data storage area is relatively small, it is possible to store the effective map data by the erasing process, and it is also possible to utilize the area other than the map data storage area, for another data, so that the application range of the storage range can be enlarged.
In another aspect of the navigation system of the present invention, the map data comprises a plurality of block map data for each unit block obtained by dividing a whole map into unit blocks, and writing and reading with respect to the storage device is performed by the block map data as unit.
According to this aspect, for example, the whole map such as an all Japan area is divided into a mesh shape, so that the map data is constructed as a set of a plurality of the block map data, as for each unit block, which is the division unit for the mesh shape. Then, this block map data is treated as the unit of accessing in the storage device. Thus, the transferring process and the erasing process of the map data may be performed in the order of the corresponding block map data by setting the unit block. Therefore, the process can be simplified.
In this aspect, all of the plurality of block map data may have data sizes same to each other.
By constituting in this manner, one block map data may be erased and then the new block map data may be immediately stored, if the erasing process is required in accompaniment with the transferring process of the map data. Therefore, the process can be even more simplified.
Also in this aspect, the map data transferring device may judge whether or not the block map data to be transferred is already stored in the storage device, and may transfer the block map data only if it is not judged to be stored in the storage device.
By constituting in this manner, when transferring the block map data, the presence and absence of the same block map data in the storage device is firstly judged. Then, only if it is absent, the block map data is transferred. Therefore, by avoiding the useless transferring process as well as the useless erasing process, a speedy navigation can be performed.
In another aspect of the navigation system of the present invention, the navigation system is further provided with a communication device for obtaining the map data to be transferred and stored to the storage device.
According to this aspect, the map data is obtained through the communication device, and is then transferred and stored to the storage device. Thus, since a device such as a map data reading device for a record medium or the like is eliminated but the communication device is used, it is possible to simplify the structure of the navigation system. Further, even in such a situation that the communication is temporarily interrupted or stopped, the navigation can be still continued by using the map data already stored in the storage device, so that the reliability of the navigation system is certainly improved.
In this case, the communication device may be a portable telephone.
By constituting in this manner, since the map data can be obtained by the portable telephone, it is possible to even more simplify the structure of the navigation system.
Also in this case, the communication device may obtain the map data through a communication network.
By constituting in this manner, since the map data can be obtained through the communication network, it is possible to even more simplify the structure of the navigation system.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.